using a trial version of SD (maybe this is the issue??) - and I would like to change the fuel units from litres to US gallons and the weights from KG to Ibs

I go to set up > change units > weight / fuel volume update the units, but when i go back into "flight details" tab for weight and balance and fuel and costings nothings changed ? 

any help much appreciated - IPad mini retina. I've tried rebooting, creating new route but the units stay the same ?